Various alloys may be characterized as being “crack sensitive”. Ingots and other workpieces composed of crack sensitive alloys may form cracks along their surfaces and/or edges during hot working operations. Forming articles from crack sensitive alloys may be problematic because, for example, cracks formed during forging or other hot working operations may need to be ground off or otherwise removed, increasing production time and expense, and reducing yield.
During certain hot working operations, such as forging and extrusion, dies apply a force to an alloy workpiece to deform the workpiece. The interaction between the die's surfaces and the alloy workpiece's surfaces may involve heat transfer, friction, and wear. One conventional technique for reducing surface and edge cracking during hot working is to enclose the alloy workpiece in a metal alloy can before hot working. With a cylindrical workpiece, for example, the inside diameter of the alloy can may be slightly larger than the outside diameter of the workpiece. The alloy workpiece may be inserted into the alloy can such that the alloy can loosely surrounds the workpiece, and the dies contact the outer surfaces of the alloy can. The alloy can thermally insulate and mechanically protect the enclosed workpiece, thereby eliminating or reducing the incidence of crack formation on the workpiece. The alloy can thermally insulates the alloy workpiece by action of the air gaps between the workpiece and the alloy can's inner surfaces and also by directly inhibiting the alloy workpiece from radiating heat to the environment.
An alloy workpiece canning operation may result in various disadvantages. For example, mechanical contact between dies and the alloy can's outer surfaces may break apart the alloy can. In one specific case, during upset-and-draw forging of a canned workpiece, the alloy may break apart during the draw operation. In such a case, the alloy workpiece may need to be re-canned between each upset-and-draw cycle of a multiple upset-and-draw forging operation, which increases process complexity and expense. Further, the alloy may impair an operator from visually monitoring the surface of a canned alloy workpiece for cracks and other work-induced defects.
Given the foregoing drawbacks, it would be advantageous to provide a more efficient and/or more cost-effective method of hot working crack sensitive alloys. More generally, it would be advantageous to provide a method for improving the hot workability of alloy ingots and other alloy workpieces.